A typical bulk carrier is a shipping vessel having a hull, within at least a major portion of at least the midbody of which, the internal volume bounded by the sidewalls and bottom of the hull, is partitioned into a plurality of cargo holds (sometimes alternatively called tanks). Depending on the vessel width and length, the cargo holds are arranged in one or more side-by-side columns extending lengthwise of the vessel and separated by longitudinal bulkheads, and a plurality of longitudinally adjacent rows and separated by transverse bulkheads. The upper ends of the longitudinal bulkheads and hull sidewalls, with associated structure, provide respective fore-aft walkways of the deck of the vessel, and the upper ends of the transverse bulkheads provide port-starboard walkways of the deck. The bottoms of the individual holds are formed by respective portions of the upper surfaces of the inner side of the bottom of the hull. Portions of the sidewalls of individual holds, whether formed by vessel hull sidewall, sides of longitudinal bulkheads or sides of transverse bulkheads are generally vertical, but may have sloped, beveled or curved regions. The holds typically are open at the top throughout an area which is, at most, substantially large as their maximum cross-sectional area. These openings, generally referred to as hatches, are normally closed during transportation, storage and waiting periods, by openable hatch covers. Hatch covers may be designed to be physically lifted out of position as a unit, or to be folded, tented or rolled out of position.
A typical bulk cargo vessel is used for transporting a flowable or pumpable commodity, without use of any containers or packaging material but for the confines of the hold. However, sometimes boxes, bags, drums, containers and other packaging confines the commodity being shipped in a hold, in quanta smaller than the bulk of a single hold.
A bulk cargo vessel may be single-hulled throughout, double-hulled throughout, or partially double-hulled (for instance, double bottomed) and the remainder single-hulled.
The walls of each side, the bottom and the top of a bulk cargo hold typically are made of steel plate, welded at edges and intersections.
The internal wall surfaces of a bulk cargo hold are subjected to at least some of the same stressful environmental conditions as is the outer surface of the vessel hull. In fact, due to the reactive or corrosive nature of some bulk materials transported, e.g., rock salt, and the confined space, the environmental stress on the wall surfaces of a bulk cargo hold can cause surface deterioration at a greater rate than is experienced by the exterior of the vessel hull. Therefore, for lengthening the economic life of the cargo vessel and keeping it in good repair, the internal surfaces of each bulk cargo hold are best cleaned and coated when the vessel is new, and then periodically recleaned and recoated.
It is possible, when fabricating a new bulk cargo vessel, to clean and coat at least some of the plates that will form respective parts of the hull and holds prior to welding the sheets together to provide the respective walls, and then, after welding, to more simply clean or reclean and coat or recoat the areas at and bordering the welded seams. There is a particularly attractive style of work if the coating being provided is a reactive (e.g., "epoxy") coating whether applied by dipping, rolling or spraying.
However, in many instances, the hold wall surfaces, like the vessel hull exterior surfaces, of a new vessel being built, are cleaned and coated entirely after cutting, welding, bolting and installation of at least some fittings have been conducted.
In both the latter instance of such new manufacture, and in ship repair and refurbishment, it has heretofore been a common practice to clean and coat the hold walls (a term which is used herein to include sidewalls whether provided by hull surfaces, longitudinal bulkhead surfaces, transverse bulkhead surfaces, the top sides of hull bottom walls and the undersides of hatch covers), using portable staging temporarily erected in the hold, possibly supplemented or replaced by use of a mobile "cherry picker" type of operator-lift temporarily lowered into the hold.
Surface cleaning typically involves forcibly impacting particles of an abrasive material ("grit") against the surface which is to be cleaned. In some instances, the particles are simply sprayed in a blast of compressed air, issuing through a hose and out of a nozzle pointed at the work surface by a human operator who is wearing protective clothing and breathing gear. In other instances, the similarly attired worker uses a pneumatically or gravity-fed centrifugal impeller the outlet opening of which they direct against the work surface.
As the abrasive grit impacts against the surface to be cleaned, it abrades away whatever is most vulnerable to its attack, principally scale, rust, caked-on remainder of former cargoes, and what remains from prior coatings applied, as affected by the environment since application. It is an operator's responsibility when abrasive blasting, to continue working on a local region of the surface, until substantially all that is `bad` is gone, but without substantially eating into what is `good`, and then moving on, to the cleaning of an adjacent or next region of the surface.
The spent grit, therefore, contains not only the material impelled against the surface, as affected by the impact, but also the removal material, all mixed together. In some instances, the work head includes a spent-grit recovery mechanism, such as an underlying catch basin or funnel and suction line, so that the abrasive blasting is conducted as a clean-up-as-you-go operation. In other instances, the spent grit simply falls to the floor, i.e., the upper surface of the bottom wall, and onto the predominately upwardly facing surfaces of staging and equipment, and is swept up, vacuumed up or otherwise collected by workers working in support of the blasting operators.
In some instances, the grit is made of sharp-grained particles of refractory material such as carborundum or agate; in other instances, it is made of hard, sharp fragments of ferromagnetic material, including bits or balls of steel. In such instances, collecting the ferromagnetic component of the spent grit separately from fragments of coating and other debris is possible, using magnetic or electromagnetic collectors or separators.
Spent grit can be fractionated and the various fractions subjected to differing benefaction, disposal and re-use procedures.
Coatings following cleanings are typically applied by spraying. Generally, these are made of what a non-technical person, and often a person in the trade speaking colloquially would call `paint`.
The current trend in coatings, is to ones which include as the vehicle or medium which enables and facilitates application, spreading and continuity of layering, yet upon completion of its contribution to the process, generates a minimum of volatile organic compounds available to escape into the air and, therefore, needing to be contained, abated, combusted or otherwise dealt with.
The staging conventionally used in holds for worker support while conducting cleaning and painting operations, typically is conventional construction scaffolding, which includes many modular sections of framework, and planking. In one sense it is convenient to use such staging, because one set of component parts can be assembled in many different combinations, in order to enable work on holds having various lengths, widths, heights and physical intrusions. However, set-up and tear-down are time consuming, and worker error in securing planks, climbing on scaffolding and dropping parts unfortunately results in accidents and injury. And, each shift of work and each set-up and tear-down involves claimbering on the scaffolding, often while carrying heavy equipment. Blasting and coating equipment needs to be assembled and taken apart, including pneumatic and liquid-delivery hoses, and electric cabling.
The copending U.S. patent application of Goldbach, application Ser. No. 08/802,676, filed Feb. 19, 1997 discloses an apparatus and method for cleaning and painting the sidewalls of a cargo hold of a bulk carrier vessel, using a vertical tower supported on the floor of the hold for being shifted in a horizontal plane. The tower supports a vertically movable trolley which, in turn, supports a horizontally shiftable, hollow rectangular, work platform which is ringed by a track. In use, the tower, trolley and platform are respectively positioned and repositioned, by shifting the above-mentioned components, in order to position and reposition a respective two runs of the track which meet at a respective corner, into various corners of the hold, at various heights, so that a worker, or a plurality of workers, operating blast cleaning and paint applicators from the respective track runs, can clean and paint virtually all of the sidewalls of the hold, whereupon the device can be lifted from the hold and lowered into another hold for performing like operations on the sidewalls of the other hold. Supply lines for grit, paint, compressed air and for ventilating the workspace are disclosed.
The copending U.S. patent application of Goldbach, application Ser. No. 08/806,097, filed Feb. 25, 1997, discloses, in addition, a remotely operable work head mountable to tracks extending along outer side rails of the work platform, so that the human workers can attend to performing the cleaning and painting operations without needing to physically support the cleaning and painting machine nozzles (against gravitational weight and against reaction or rebound forces due to energetic contact of the impelled abrasive grit and sprayed paint against the ship hold sidewall surfaces).
The present invention extends the usefulness of the self-contained device for cleaning and coating hold surfaces in a bulk carrier, including modifications to and elaborations upon the apparatus and methods disclosed in Goldbach et al applications Ser. Nos. 08/802,676 and 08/806,097.